The present invention pertains to pharmaceutical injection devices, and, in particular, to a mechanism used to delay needle retraction for an automatic injection device.
Patients suffering from a number of different diseases frequently must inject themselves with pharmaceuticals. A variety of devices have been proposed to facilitate these injections. One type of device is an automatic injection device. This type of device, when triggered by a user or someone helping the user, automatically inserts into the user a needle of a syringe that prior to triggering was disposed within the device housing, and then automatically injects a dose of medication through that inserted needle. One known type of automatic injection device then automatically advances a shroud to cover the needle when the dose is completed. In another type of automatic injection device having a configuration more desirable to some, and instead of having an advancing shroud, the device will automatically retract the needle into the housing when the dose is completed. To ensure that the full desired contents of the syringe have been injected prior to the syringe being retracted, a variety of differently configured delay mechanisms have been proposed for such automatic injection devices.
One problem with at least some automatic injection devices having delay mechanisms is that the devices are longer than some users may like when placed by the user on an injection site. All things being equal, a shorter device for a given delivery volume may be provided by making the syringe shorter but with a larger diameter. However, as causing such syringes to inject tends to require the application of more force and therefore a more robust drive system, constraints can result as to where the delay mechanism can be accommodated within the device housing. Still further, some delay mechanisms are not as compact axially as would be desirable to allow for the injection devices in which they are used to be short or compact.
Another problem with at least some automatic injection devices having delay mechanisms is that the means for holding the needle in a retracted position after use is less reliable than desired. It is possible with such devices for the needle to be released accidentally from a locked position after use despite the device experiencing a relatively minor impact or external force.
Thus, it would be desirable to provide an automatic injection device that can overcome one or more of these and other shortcomings of the prior art.